MECHANICAL PROPERTIES OF THE 38KhS STEEL AFTER ISOTHERMAL QUENCHING IN THE BAINITIC TEMPERATURE REGION
The mechanical properties of the sparingly alloyed 38KhS steel with a carbon content of 0.36 % and a silicon content of 1.14 % after different isothermal quenching regimes in the bainitic temperature range with different holding times were investigated. It is demonstrated that, after such heat treatment, the structure of carbide-free bainite represented as a two-phase mixture of carbon-depleted bainitic ferrite and carbon-enriched retained austenite with different morphology are formed in the steel. Retained austenite in such carbide-free bainite is substantially enriched with carbon and contains a considerable part of the total carbon content in the steel. It is shown that tempering for 1...2 hours at a temperature of 300 °С raises the values of impact strength of the 38KhS steel after isothermal holdings in the bainitic transformation temperature range resulting in the formation of different proportions of lower lath and upper globular bainite, retained austenite and martensite in the structure. It has been found that, under such tempering, stabilization of retained austenite occurs due to noticeably increased carbon content in it.
Keywords: isothermal quenching, carbide-free bainite, retained austenite, bainitic ferrite, carbon, mechanical properties, strength, impact strength